HUNTSVILLE - Scientists at the Marshall Space Flight Center are working on a key problem of sending people on long-term trips into space - protecting them from dangerous doses of radiation.

When President Bush announced a new quest to go back to the moon and eventually on to Mars, he noted the dangers space-travelers will face.

"The environment of space is hostile to human beings," Bush said. "Radiation and weightlessness pose dangers to human health, and we have much to learn about their long-term effects before human crews can venture through the vast voids of space for months at a time."

NASA has worked for years on protecting astronauts from radiation. But Administrator Sean O'Keefe said Wednesday that understanding how the human body responds to long periods in space, and how to mitigate the effects, will become the agency's top research priority, especially at the International Space Station.

"We're reordering ... the very specific emphasis on the research on station to emphasize life science, human physiology, (and) the human effects and consequence of long-duration space flight," O'Keefe said. "This will become the primary, almost singular focus of our research agenda in the time ahead."

The space agency decided about a year ago to focus its radiation-protection efforts through a program based at Marshall.

"We're looking for innovative materials sources to protect the astronauts from damaging radiation" said Ed Semmes, program manager of the Space Radiation Shielding Program, which was created in February 2003. Scientists at other NASA centers, the Department of Energy and universities around the country are involved in the research.

Last fall, NASA commissioned the $34 million Space Radiation Laboratory at the Department of Energy's Brookhaven National Laboratory in Upton, N.Y. The lab is designed to simulate the radiation astronauts encounter in space.

The first material produced by the Space Radiation Shielding Program and tested at the lab was reinforced polyethylene, developed by Marshall scientist Raj Kaul.

Water is a good shield against radiation, and scientists have been using it as a benchmark for the level of protection they are seeking in new materials, Semmes said. Tests show that reinforced polyethylene "behaves very closely to what water does," he said.

Reinforced polyethylene eventually could replace the traditional aluminum skin of spacecraft, Semmes said. "It's about 10 times stronger than aluminum per unit weight," he said.

Because of its strength, reinforced polyethylene also could help in protecting the spacecraft from strikes by small meteoroids, Semmes said. Material that can serve multiple purposes is a key for long-duration missions, Semmes said, because fewer protective layers means less weight.

Spacecraft such as the International Space Station traditionally have been made of aluminum covered with insulation and shields to protect them from meteoroids and other debris.

Other research in the Space Radiation Shielding Program includes work at NASA's Langley Research Center on a radiation shield of foam between two panels of lightweight composite material, Semmes said.

The shielding program is working toward developing a suite of materials by 2008 and a tool for assessing their effectiveness in various circumstances, Semmes said. An informal goal is to deliver a new material every year, he said.

"We would hope to have four to six material design solutions by the time we get to 2008," he said.

The Space Radiation Shielding Program started with an annual budget of $4 million, Semmes said. It will get roughly $6 million this year and level out at around $7 million next year.

A six-month stay on the space station exposes the crew to the equivalent about 600 chest X-rays, more or less depending on how active the sun is during that period, Semmes said.

An astronaut on a mission of several months or more outside Earth's protective magnetic field and ionosphere would face dangerous doses of radiation without protection, Semmes said. "For travel beyond the station, the crew will be exposed to the full intensity of galactic cosmic rays, potentially resulting in the damage to cell tissue and altering genetics, leading to disease such as cancer," he said.

The Space Radiation Shielding Program was started as part of NASA's Space Radiation Initiative. A goal of that initiative is to ensure crews can staff the space station for up to three six-month missions or eventually a 1,000-day mission beyond Earth's orbit without going over radiation exposure limits recommended by the National Council for Radiation Production, according to a NASA press release.

Astronauts who walked on the Moon about 35 years ago didn't face the radiation problem because their missions lasted only a few days, Semmes said. "They just weren't out there long enough to get the exposure," he said.